(i) Field of the Invention
This invention relates to an emulsifying composition and more particularly, to an emulsifying composition which comprises an hydroxyalkyl or alkenyl phosphate or a salt thereof thereby ensuring good feeling to the touch and low irritation when applied to living body and particularly skin withh excellent emulsification stabilizing ability.
(ii) Description of the Prior Art
In general, compounds used as an emulsifier can broadly be classified into two groups including a hydrophilic emulsifier group which shows high solubility in water or has a great HLB value and an oleophilic emulsifier group which shows high solubility in oil or has a small HLB value. The former has conventionally been used for stabilizing mainly O/W type emulsions and the latter used for W/O type emulsions. In this connection, however, oils to be emulsified greatly vary in property depending on the type of oil and thus a required level of HLB also depends on the type of oil. Accordingly, there is little chance of using hydrophilic emulsifiers alone or oleophilic emulsifiers alone and it is general to use a mixture of both the type emulsifiers to have a suitable level of HLB value. Especially when oils to be emulsified are in the form of a mixture, such a general way of the use is the common practice.
Conventionally employed hydrophilic emulsifiers are, for example, surface active agents which include anionic surface active agents such as alkali metal salts of fatty acids, alkylsulfates and the like, and ethylene oxide-added nonionic surface active agents such as polyoxyethylene alkyl ethers, polyoxyethylene fatty acid esters, polyoxyethylene sorbitan fatty acid esters, and the like. On the other hand, oleophilic emulsifiers include, for example, nonionic surface active agents such as sorbitan-fatty acid esters, glycerine-fatty acid esters and the like.
A method of preparing emulsifier compositions having different HLB values by mixing hydrophilic emulsifiers, which are obtained by combining fatty acid-triethanolamine salts and ethylene oxide-added nonionic surface active agents, with oleophilic emulsifiers such as glycerine-fatty acid esters has been widely utilized for emulsification in order to obtain emulsion-type cosmetics such as creams, lotions and the like.
However, it has been suggested that ethylene oxide-added nonionic surface active agents contain formalin, dioxane and the like as impurities and these impurities have the alergic action on living body. Further, it is known that anionic surface active agents are generally high in skin irritativeness and are thus not favorable as an emulsifier. Accordingly, in case that the anionic surface active agents are employed, alkali metal salts of fatty acids are used by virtue of giving relatively low skin irritativeness, this case however, accompanied by another disadvantage that the resulting emulsion is rendered alkaline.
That is, emulsion-type cosmetics using these known emulsifiers are not fully satisfactory in safety.
On the other hand, it has been known that there are present in living body a group of compound having surface activity and called phospholipids, which play an important role as main components of membranes of living body. Typical examples of the phospholipids include glycerophospholipids such as phosphatidyl choline (lecithin), phosphatidyl ethanolamine (cephalin), phosphatidyl serine and the like. These phospholipids are components in vivo, and are thus surface active materials which are high in safety against living body. For instance, lecithin has been industrially utilized as an emulsifier. However, since these are of natural origin, they have various impurities and suffer deterioration in quality inherent of natural materials as time goes. Furthermore, the structure such as of a fatty acid composition cannot be arbitrarily changed, so that its HLB value cannot be changed freely. Moreover, in order to obtain emulsified cosmetics which ensure good feeling on use, it is known that relatively hydrophilic oils or polar oils are satisfactorily used as the oil phase. However, the emulsification of polar oils is comparatively difficult and sufficient emulsification stability cannot be obtained in case of using weak surface active materials such as lecithin.